Lithium ion cells have become widespread and popular since the introduction of the first commercial rechargeable lithium battery in 1991. The high energy density of lithium ion cells makes them ideal for use in portable devices, including cell phones, portable computers, and electric/hybrid electric vehicles.
A lithium ion cell is composed of four key components: a cathode, an anode, a separator, and an electrolyte. As the cell charges, the cathode is oxidized to provide lithium ions and electrons to the anode. During discharge, the cathode is reduced back to its original state, while at the same time the anode is oxidized to provide lithium ions and electrons. The separator prevents the cathode from directly contacting the anode thereby creating a short circuit. At the same time, the separator allows current-carrying ions to pass from the cathode to the anode and vice-versa. The electrolyte provides a path for the lithium ions to travel between the cathode and the anode.
Typically, the above components are held within a sealed case. The case includes a safety vent to prevent abnormal pressure from building up inside the lithium ion cell during discharge, charging, and during a short circuit. There are three main types of lithium ion cell case structures, namely, cylindrical, prismatic, and pouch-style.
A lithium ion cell typically generates a voltage of 3 to 4 volts. To construct a battery of higher voltage, it is necessary to connect individual cells in series externally to form a battery pack of the desired voltage. Lithium ion cells can also be connected in parallel to increase the amount of current that the battery pack can provide.
A typical lithium ion battery pack includes a battery management system. The purpose of the battery management system is to avoid overcharging and over-discharging individual cells within the battery pack.
The need exists for a lithium ion battery that is easier and less costly to construct than existing batteries.